This invention relates to improvements in clamp assemblies for steering column assemblies, especially but not exclusively to electric power assisted steering assemblies. In particular it relates to clamp assemblies for steering column assemblies adjusted for both rake and reach.
It is known to provide a steering column assembly in which a steering wheel is connected to one or more road wheels through a collapsible or telescopic steering column shaft. The shaft is designed to collapse away from a driver of the vehicle if a load is applied to the steering wheel in the event of an accident. The shaft may comprise a single part shaft, which has a weakened central section that will concertina under an axial load. Alternatively it may comprise a two part telescopic shaft in which one part slides axially into the other under an axial load.
To locate the steering shaft relative to the vehicle it is typically supported within one or more bearings carried by an adjustable support portion, often referred to as a steering column shroud. The shroud is in turn secured to a fixed portion bolted or otherwise fixed to a conveniently accessible part of the vehicle chassis or bulkhead.
In many vehicles produced today the column shroud, which may for convenience be thought of as an adjustable portion, is releasably locked to the fixed portion of the vehicle in a way that permits the steering shaft to be adjusted for rake (up and down) and reach (in and out). A lever-which must be located within easy reach of the driver-allows a clamping mechanism to be locked and unlocked for the position of the steering column shroud to be adjusted. This enables the driver of the vehicle to set the steering wheel at the most comfortable position.
With the introduction of steering wheel mounted airbags there has recently been a demand that, once adjusted, the column must be held in place by a positive locking method. By this we mean that, when the clamp mechanism is moved into its locked position, there must be greater restraint against subsequent column movement for reach than would be created solely by friction.
It is normal to increase the resistance to movement by providing for a toothed engagement between the fixed portion and a clamp assembly and similarly between the clamp assembly and the adjustable portion. However, a basic problem with the use of teeth in this way is that on occasions the tips of the teeth on one part may be exactly in line with the tips of the teeth that should engage them when the driver attempts to move the clamp to the locked position. This so called tooth-on-tooth problem can either prevent the driver locking the clamp properly or in extreme cases damage the teeth or the locking mechanism.